Iris reflectance measurements in >1000 healthy adult twins: exploration of heritability and associations with eye color

Abstract

Purpose : Eye color is highly heritable, and some ocular diseases can be associated with changes in levels of iris pigmentation. In this study, we explored iris reflectance measurements made with a portable device in adult twins, exploring intra-pair correlations and investigating whether these differed significantly between eye colors.

Methods : Healthy adult volunteers were recruited from the TwinsUK cohort. Participants underwent undilated photopic electroretinogram recordings using a portable electroretinography device (RETeval, LKC Technologies Inc., Gaithersburg, MD, USA) as part of a large electroretinography study. During recordings, the device captured a video image of the participant’s eye. Iris pixel intensity (divided by that recorded from the pupil) was extracted from this image by the device’s software. We quantified coefficients of intra-pair correlation for monozygotic (MZ) and dizygotic (DZ) twin pairs. Qualitative iris color was also noted (blue, grey, green, hazel, light brown or dark brown). Measurements were compared between iris color categories (one-way ANOVA).

Results : Recordings and images were obtained from 1626 participants. After exclusion of singletons, data was available from 1374 twins (454 MZ and 233 DZ pairs). 84% were female. Mean (SD) age was 53.6 (16.2) years for the whole cohort. Coefficients of intra-pair correlation were 0.75 and 0.44 for MZ and DZ pairs respectively. Mean measurements differed significantly (p<0.05) between eye color categories for 10 out of 15 pair-wise comparisons (the following comparisons were not significant: blue-grey; blue-green; grey-green; green-hazel; hazel-light brown).

Conclusions : Iris reflectance ratio measurements, as quantified by the portable device, showed greater intra-pair correlation for MZ than DZ pairs, implying significant heritability. These measurements also differed significantly between eye color categories, suggesting possible utility as a continuous quantitative trait relating to iris pigmentation.

This is a 2020 ARVO Annual Meeting abstract.